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Actually there is no 24V at all. Here is the full circuit of the SSR unit:Attachment 19864
So, the potentiometer (VR1) works as a rheostat, and there is no galvanic decoupling; thus the variable resistor is under the same 120V line voltage.

By the way, we already successfully got the appliance certified per CE applicable requirements, with the same SSR unit and a few dollar potentiometer. For that point, CE certification has less strong restrictions regarding critical components.

[QUOTE]

Now you're talking.

The DIAC is an integral part of the SSR (dimmer) which in turn drives the TRIAC that controls the high energy 1800 watt load.

This component is housed in a single housing that is common to household dimmers. Since this is a run-of-the-mill consumer item (generic if you will), I would assume some of them passed UL testing lab.

So, how much trouble would it be to just mount the dimmer inside an NEC/UL Listed enclosure and have the return lead drive the TRIAC. This will take running two conductors to the dimmer which will give you all the options to do it inside the realm of NEC/UL.

Keep in mind that it is none of my business telling you how to build the unit. As an engineer yourself, you know of several heuristic approach in tackling with a problem—I'm just telling you what's available out there.

It would look like a jerry-rigged set-up especially with light dimmer controlling a cotton candy-making machine.

Perhaps it will be a conversational piece if the machine were installed where tourists were milling about leisurely, appreciating the creativity involved.

Note that common run of the mill lighting dimmers use a line powered circuit and a cheap looking potentiometer (rotating or linear).
Whatever they use must be sufficient to allow the final product to be UL listed in its category. In some but not all cases there is a plastic shaft connecting to the pot rather than a metal shaft.

Always the shell and shaft on the pot is at ground potential. That would be another possibility for the design of this controller as long as the designed isolation between the shell and the energized parts of the pot well exceed 120v.

The DIAC is an integral part of the SSR (dimmer) which in turn drives the TRIAC that controls the high energy 1800 watt load.
This component is housed in a single housing that is common to household dimmers. Since this is a run-of-the-mill consumer item (generic if you will), I would assume some of them passed UL testing lab.
So, how much trouble would it be to just mount the dimmer inside an NEC/UL Listed enclosure and have the return lead drive the TRIAC. This will take running two conductors to the dimmer which will give you all the options to do it inside the realm of NEC/UL.

I'm not sure if I got your idea right. The unit I was talking about is UL recognized and it contains both DIAC and TRIAC components in the same enclosure. It may look like a household light dimmer since it has similar circuit; it is rated for 25 Amps, though. Anyway, having TRIAC separated from DIAC won't resolve the issue of the pot under the line voltage.

Originally Posted by myspark

Keep in mind that it is none of my business telling you how to build the unit. As an engineer yourself, you know of several heuristic approach in tackling with a problem—I'm just telling you what's available out there.

That is ok for me! Otherwise I wouldn't have this thread posted here. I appreciate all thoughts and suggestions I got at the forums.

Originally Posted by GoldDigger

Have you looked at the possibility of using a low voltage supply and an opto-isolator?. Not cheap, but lower cost than a $200 component.

Yes, it was plan B. I have already checked this possibility, the same manufacturer offers a unit (rated same 25Amps) with opto-isolator. So I will need a power supply unit to energize control circuit. You are correct, it will increase the price, but not such drastically. The main idea of this thread was to get know if there is a way to have the same circuit as we have for European version. But now it seems that the circuit for North America version must be revised.